Chemistry. Chemistry is the study of the interactions between atoms and molecules. Atoms and Molecules

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1 Chemistry Chemistry is the study of the interactions between atoms and molecules. Atoms and Molecules An atom is a particle of matter that cannot be further divided without changing the chemical identity of the atom. The word atom derives from the Greek word meaning uncuttable. Atoms are comprised of protons, neutrons, and electrons. There are ~ 09 different kinds of atoms. The different kinds of atoms are called elements.

2 Examples of Atoms H Hydrogen He Helium C Carbon Cu Copper O Oxygen Au Gold N Nitrogen Ag Silver Na Sodium Mg Magnesium Fe Iron Cl Chlorine U Uranium Ne Neon Atoms and Molecules A molecule is a compound composed of two or more atoms. The atoms may be of the same element or of a combination of different elements. Most of the matter we see in the universe is comprised of molecules.

3 Examples of Molecules H O CO NaCl C H O N O Water Carbon Dioxide Sodium chloride (table salt) Sucrose Nitrogen Ozone Changes in Matter Physical Change: When a substance undergoes a physical change, its molecular identity remains the same. Chemical Change: When a substance undergoes a chemical change, the atoms in the substance are rearranged or exchanged with another substance to form new atoms or molecules.

4 Mass Physical Properties of Matter Mass is an intrinsic property of an object it is a measure of how much material is in the object. Mass and weight are not the same thing: weight is the gravitational force exerted on an object by another body (such as the Earth): w = m g (w = weight; g = acceleration due to gravity) Physical Properties of Matter Mass (con t.) We often incorrectly refer to the mass of an object as its weight we say we are weighing something when we are really determining its mass. You can tell if you are measuring mass or weight by the device used any device employing a spring determines weight; any device comparing forces, such as a balance, determines mass.

5 Physical Properties of Matter Mass (con t.) The units for mass are grams (or any multiple of grams such as kilogram, milligram, etc.) A pound is actually a unit of weight, but in common usage, we can think of it as a mass unit: kg =.0 lbs. Mass does not change with pressure or temperature. Physical Properties of Matter Volume Volume is a measure of the space occupied by an object. Volume depends not only on the amount of material in the object, but also on the pressure acting on the object and the temperature of the object. Units of volume are length cubed: cm = ml, 000 ml = L, etc.

6 Density Physical Properties of Matter Density is related to what we usually refer to when we talk about something being heavy or light. Definition: density = mass/volume units = g/ml (typically) Physical Properties of Matter Density Table. lists density of some common substances. Density is also a function of temperature and pressure because volume changes with temperature and pressure. Which is more dense a solid, a liquid or a gas? Why does ice float on water?

7 Time Physical Properties of Matter Time is needed to determine such quantities as the energy of a system or the rate of a chemical reaction. Units of time are second, (s), or multiples of seconds (millisecond [ms], microsecond [ s], nanosecond [ns], etc.). Physical Properties of Matter Temperature Temperature is actually a measure of the internal energy of an object. The higher the temperature, the more internal energy an object possesses. In science, temperature must be measured on an absolute scale with a defined value of zero below which temperature may not fall.

8 Physical Properties of Matter Temperature (con t.) Both Celsius and Fahrenheit temperature scales do not satisfy this requirement each may have negative values of temperature. Absolute zero is the lowest temperature attainable by an object this corresponds to the minimum possible internal energy of an object. In practice, we may never reach absolute zero. Physical Properties of Matter Temperature (con t.) The absolute temperature scale uses units of degrees Kelvin (abbreviated K) K = -. o C The size of one degree Kelvin is the same as one degree Celsius. When performing calculations involving temperature, if you use degrees Kelvin, you will always be safe. 8

9 Physical Properties of Matter Temperature (con t.) Sometimes we use the change in temperature, T, to calculate some properties of a chemical system, where: T = T final T initial In this case, you may use either K or o C because the size of the units are the same. The mks Unit Set We use SI (Systeme Internationale, or metric) units in science. The standard set of units used by most chemists is the mks set: meter/kilogram/second. Many other units are defined relative to these fundamental quantities. Example: J (joule) kg m s - There is also the cgs set of units that is sometimes used: centimeter/grams/second 9

10 Significant Figures When writing a number, it is important to know how well the value of the number is known. Examples If I say I have donuts, I usually mean I have exactly donuts because donuts do not come in fractions of a unit. Significant Figures If I say I have grams of salt, does that mean exactly grams or something between. and. grams. Because the mass of an object in grams may be expressed in fractions of grams, I must specify as precisely as possible what the mass is. Significant figures indicate the precision with which a number has been determined. 0

11 Significant Figures When expressing a value, the number of digits used indicates the number of digits that could be measured accurately. The final digit in the value is an estimate of the least precise number. Length =. units Significant Figures The manner in which a number is written indicates the number of significant figures it has. Examples 000 significant figure as written, the zeros are simply place holders and do not indicate precision of the measurement. the true value is between 00 and 00

12 Significant Figures 000. By placing a decimal point after the last zero, this indicates that the zeros were measured significant figures the true value is between 999. and 000. Significant Figures zeros following the decimal point with no other digits behind them also indicate precision of measurement, so they count as significant figures significant figures the true value is between and

13 Significant Figures.000 for small numbers less than one, zeros following the decimal point before the first digit are simply place holders and do not indicate precision significant figure the true value is between.000 and.000 Significant Figures zeros following digits in small numbers indicate precision and are significant. significant figures the true value is between and.00000

14 Mathematical Rules for Significant Figures Addition/Subtraction When adding or subtracting numbers, the number of significant figures in the result is determined from the position relative to the decimal point of the least significant figure of the numbers being added or subtracted: Mathematical Rules for Significant Figures Add.,.9, and Because. has only sig. fig. after the decimal point, the final answer can have only sig. fig. after the decimal point the correct answer is.

15 Mathematical Rules for Significant Figures Subtract.9 from 8000: Because 8000 has only sig. fig. four places to the left of the decimal point, the least significant figure in the final answer must also be four places to the left of the decimal point correct answer is 8000 Mathematical Rules for Significant Figures Multiplication/Division The number of sig. figs. in the result is determined from the number of sig. figs. in the least significant value used in the calculation:

16 Mathematical Rules for Significant Figures Multiply 88.0 by x has sig. figs. and.00 has sig. figs. This limits the result to a total of three sig. figs. the correct answer is 0. Scientific Notation It can be very cumbersome to write very large or very small numbers using zeros as place holders: m proton = g c (speed of light) = m s - mole = molec

17 Scientific Notation Instead, we use scientific notation to express the zeros in powers of ten: m proton =. x 0 - g c (speed of light) =.998 x 0 8 m s - mole =.0 x 0 molecules Rules Add one power of ten when moving the decimal point one position to the left. Subtract one power of ten when moving the decimal point one position to the right. Scientific Notation 90 = 9. x 0 = 9. x 0 = 9. x =.8 x =.0 x 0 - =. x 0 - =. x =. x 0 -

18 Prefixes Prefixes on units of measurement are used to simplify expression of large or small numbers they replace the use scientific notation in some cases: giga (G) = 0 9 micro ( ) = 0 - mega (M) = 0 nano (n) = 0-9 kilo (k) = 0 pico (p) = 0 - centi (c) = 0 - femto (f) = 0 - milli (m) = 0 - The Periodic Table The Periodic Table arranges the elements according to their properties structural (the manner in which the protons and electrons are arranged) and chemical (the properties resulting from the arrangement of the electrons, principally) The Periodic Table has seven rows and columns. 8

19 The Periodic Table The Periodic Table Alkali Metals Lithium Sodium Potassium Rubidium Cesium Francium 9

20 The Periodic Table Alkaline Earth Metals Beryllium Magnesium Calcium Strontium Barium Radium The Periodic Table Transition Metals Copper Gold Silver Platinum Chromium Zinc Tungsten etc. 0

21 The Periodic Table Lanthanide Metals Lanthanum Cerium Praseodymium Neodymium Promethium etc. The Periodic Table Actinide Metals Actinium Thorium Uranium Plutonium etc.

22 The Periodic Table Halogens Fluorine Chlorine Bromine Iodine Astatine The Periodic Table Noble Gases Helium Neon Argon Krypton Xenon Radon

23 The Periodic Table Main Group Elements Carbon Oxygen Nitrogen Sulfur Aluminum Silicon Lead Tin etc. Main Group also includes Alkali, Alkaline Earth metals, Halogens, and Noble gases. The Periodic Table H The Metals B Al Si Ge As Sb Te Po At

24 The Periodic Table H The Metalloids B C Al Si P Ge As Se Sb Te I Po At Rn The Periodic Table H The Non-Metals He B C N O F Ne Al Si P S Cl Kr Ge As Se Br Ar Sb Te I Xe Po At Rn

25 The Periodic Table As you move from left to right in a given row of the Periodic Table, the elements get heavier (not necessarily larger). The chemical properties also undergo significant change when moving between columns of the Periodic Table. The Periodic Table As you move down a column in the periodic Table, the elements increase in mass and size, but the chemical properties do not change dramatically between rows.